The present invention is directed generally to a light dispersing film and a method of manufacture, and particularly to a beaded light dispersing film.
Beaded light dispersing films are used with rear projection screens and monitors for transmitting an image from one side of a screen to a viewer on the other side. Such films typically include a number of small beads attached to a substrate film, and an opaque layer disposed between the beads so that whatever light is not transmitted through a bead is absorbed by the opaque layer. The opaque layer also absorbs ambient light incident on the film from the viewer""s side, thus reducing the background light detected by the viewer.
Dispersing films are characterized by the gain, resolution, transmission, ambient light rejection and contrast, which properties are determined by the structure and materials employed in its construction. The gain is a measure of the intensity of the light transmitted by the film as a function of angle measured from normal incidence, and is determined, at least in part, by the refractive index of the beads and the surrounding material. The viewing angle of a particular film is defined as that angle at which the intensity is half the intensity of the light transmitted on-axis. The resolution of the film is determined, at least in part, by the size of the beads. Ambient light rejection and contrast are affected by absorption of the opaque layer.
The interdependence of the optical properties of the various components of the film limit the optimization of the film characteristics. There is, therefore, a need to overcome this interdependence so that new films may be produced having superior characteristics of gain, resolution, efficiency, ambient light rejection and contrast.
Generally, the present invention relates to a light dispersing film and its method of manufacture. In one embodiment the film has an optically transparent layer and optically transmitting beads arranged to penetrate at least partially into a first surface of the transparent layer to define clear apertures at interfaces between the beads and the transparent layer. An absorbing layer is disposed on the transparent layer, in interstices between the beads. The beads penetrate into the transparent layer to a depth selected to substantially achieve maximum transmission of light through the optically transmitting beads, while maintaining essentially optimum contrast for the maximum light transmission.
In another embodiment, the film includes a layer of optically transparent material having a support surface and a plurality of beads of optically transmitting material having a selected shape and refractive index and arranged in a single-layer array on the support surface, each bead at least partially disposed within the layer of optically transparent material to produce an interface therewith, the interface defining a clear exit aperture. A layer of light absorbing material having a selected thickness is affixed to the layer of optically transparent material, for controlling ambient light rejection of the light filter and to reduce light transmission through interstices formed by the plurality of beads. The beads penetrate into the layer of optically transparent material to a depth selected to substantially maximize transmission of light through the plurality of beads.
In another embodiment, the film includes optically transmitting beads arranged to penetrate at least partially into a first surface of a transparent layer. The beads define clear apertures at interfaces between the beads and the transparent layer. An absorbing layer is disposed on the transparent layer, in interstices between the beads, and a transparent cover layer is disposed over the absorbing layer and the optically transmitting beads.
A method of manufacturing the film includes disposing optically transparent beads partially into an optically transparent layer, a bead penetration depth into the optically transparent layer being selected to substantially maximize light transmission through the optically transparent beads, an absorbing layer overlying the optically transparent layer.
The above summary of the present invention is not intended to describe each illustrated embodiment or every implementation of the present invention. The figures and the detailed description which follow more particularly exemplify these embodiments.